Apple today released watchOS 5.1.2, the third update to the watchOS 5 operating system that runs on modern Apple Watch models. watchOS 5.1.2 comes one month after the release of watchOS 5.1.1, an update that introduced new emoji and color watch faces and addressed a bricking bug that had been introduced with watchOS 5.1.

watchOS 5.1.2 can be downloaded for free through the dedicated Apple Watch app on the iPhone by going to General –> Software Update. To install the new software, the Apple Watch needs to have at least 50 percent battery, it needs to be placed on a charger, and it needs to be in range of the iPhone.

watchOS 5.1.2 introduces the long-awaited ECG feature for Apple Watch Series 4 models in the United States. The ECG functionality works through electrodes built into the back of the Apple Watch Series 4 and the Digital Crown, allowing users to take a single-lead electrocardiogram with the wrist-worn device. An ECG measures the electrical activity of the heart and is often used to diagnose heart conditions.

Alongside ECG functionality, watchOS 5.1.2 introduces a new feature that will let you know if the Apple Watch is detecting an abnormal heart rhythm that’s indicative of atrial fibrillation, which can be a sign of a serious health problem. The ECG feature is limited to the Series 4, but the irregular heart rhythm notifications will be available on all Apple Watch models able to run watchOS 5 – that’s Series 1 or newer.

The watchOS 5.1.2 update also brings new complications for the Infograph watch faces on the Apple Watch Series 4. Complications that have been added include Mail, Messages, Home, Maps, Apple News, Find My Friends, Phone, and Remote, all of which can now be assigned to the available complication slots on the Infograph watch face.

With most of these complications, the icon is designed to provide quick access to opening up an app rather than relaying information like unread messages or emails.

watchOS 5.1.2 also includes a new toggle in Control Center for turning the Walkie-Talkie feature on and off, which makes it a lot easier to disable Walkie-Talkie when it’s not in use and turn it back on when it’s needed.

Apple’s release notes:

This update includes new features, improvements and bug fixes:

– New ECG app on Apple Watch Series 4 (US and US territories only)

* Allows you to take an electrocardiogram similar to a single-lead electrocardiogram